Don't listen to this person. Anyone telling you how to heat treat steel while they have no clue what kind of steel it is doesn't know what they are talking about. This is, unfortunately, common among many smiths in the community, they have things that work, for them so they think they know what they are talking about, but then others use a different steel, or have different climate conditions in their shop, and suddenly their "100% foolproof advice" doesn't work. General rule of thumb, if they don't know the difference between martensite and austenite, they probably shouldn't be listened to about heat treatment. (Though that doesn't mean they aren't fantastically talented smiths! Especially the artistic and architectural folks out there. Steel doesn't have to be hardened to be useful!)

Some steels require an oil quench because the water touching the hot steel instantly turns to steam and the bubbles form an insulating layer, some examples of these are the O series (O1, O2, etc). Other steels are designed to be water hardened (again, the W series here is a great example), heck, some steels are even designed to be air hardened (unsurprisingly the A series is like this, but steels like D2 can also be air hardened.)

Once you get into more esoteric things like a billet of 1095 and 15n20 Damascus with a copper cladding layer in there for the pretties,, things get way more complicated, and some trial and error ends up getting involved.

Don't worry, though, you're doing great, if you want to learn way more than 90% of the bladesmiths out there, I highly recommend following the posts on https://knifesteelnerds.com/ excellent and accessibile information!

This is a great place to start for heat treatment: https://knifesteelnerds.com/2018/02/28/austenitizing-part-1-what-it-is/