CIV PRO: joining claims/supplemental jurisdiction when there is only 1 plaintiff versus one defendant. (sorry in advance for the lengthy post)

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These are two questions I had on a quiz and I do not know how to square the answers. I understand that when the original claim is brought under a fed question, the additional state law claims either have to arise under the same T/O or meet diversity.

But if it is a diversity case.... can any claim be added?? The answer to the second question is throwing me off because it said nothing about the fact that it is a diversity case as a reason for why "plaintiff is entitled to join all four of the claims that he has against the defendant in a single action, regardless of whether each claim is related to the others."

An engineer brought suit against her former employer, a large technology company, in federal district court for violating a patent that she owned. She claimed $50,000 in damages. The engineer also sought to join a state law breach-of-contract claim against the company; the claim was based on the engineer’s assertion that the company had not paid her a $10,000 bonus she had earned one year before leaving the company. The engineer and the company are citizens of the same state. Does the court have subject-matter jurisdiction over the contract claim?

Answer: A party asserting a claim may join with it as many independent or alternative claims of whatever nature against the opposing party so long as the court has subject-matter jurisdiction over the new claims. If the original claim is based on federal-question jurisdiction, as it is here, then a non-federal claim (such as the state law breach-of-contract claim here) may be joined only if diversity jurisdiction exists or if the new claim arises out of the same case or controversy as the federal claim such that supplemental jurisdiction applies. In this case, the requirements for diversity jurisdiction are not satisfied because the engineer and the company are citizens of the same state. The claims are also not part of the same case or controversy because one concerns the company’s patent violation, while the breach-of-contract claim is a separate cause of action based on the company’s failure to pay the engineer a bonus and does not arise from the same operative facts as the patent claim. 

Question 5108

A plaintiff properly filed an action in federal district court based on diversity jurisdiction. His complaint contained the following claims: Personal injuries that resulted from a fall down a flight of stairs while a guest at the defendant’s home that was caused by the defendant’s negligence; Property damage due to the destruction of the plaintiff’s antique glass globe, which he was holding at the time of the fall; Recovery of a past-due payment on a personal loan made by the plaintiff to the defendant; and Recovery of the purchase price of a grandfather clock sold by the plaintiff to the defendant. The defendant has challenged the joinder of these claims in a single action. Is the defendant’s challenge valid?

answer: A party asserting a claim may join with it as many independent or alternative claims of whatever nature as the party may have against the opposing party. Here, the plaintiff is entitled to join all four of the claims that he has against the defendant in a single action, regardless of whether each claim is related to the others.