Does the vinyl have to be heat pressed?

I noticed last time I was in this custom tshirt store bugging the guy, he didnt press the vinyl cut he just made. I didn't get a chance to ask him. ??

Sort of a prelude to my next question. I dont have a plotter/cutter and I found some people in my area that make signs but not tshirts. Before going into details with them about the differences in sign vinyl and the heat transfer vinyl I wanted to understand it myself. Was the store being cheap by adding sign vinyl to the shirt? Does that even wash and still stick? OR is that normal or a different kind of vinyl? I am assuming none of the people I contacted would have the heat transfer vinyl, so should I be adamant about using heat transfer vinyl only or does the sign vinyl work the same for tshirts?

I hope my question is clear and not too silly. I realize they are different but its unclear considering what I saw.

Thanks

Bob