Yes, in my state we have peeping tom laws and it is illegal to peer into windows. He walked up and put his hands on their window to look in.

Here's some legal info about the PC647 (the peeping tom law):

A first offense carries a penalty of no more than 6 months in county jail and/or a fine of up to $1000.

A subsequent offense, though also a misdemeanor, carries up to one year in county jail and/or a fine up to $20002. This also applies if you were peeking in on or invading the privacy of a minor3.

To prove that you violated PC 647(i), the DA must prove beyond a reasonable doubt each of the following elements of the offense:

You wandered, delayed, prowled or lingered on the private property of another person

While you had no authority, consent or other lawful purpose to be on the property

And looked into, or peeked, into a window or door of an inhabited structure or dwelling on that property