shounen ai translates to boy love and it is definitely a different genre from yaoi,, I've learned when avoiding manga with implicit content to completely avoid any yaoi tags
Im largly speculating here but
if your friend wants an idea hmm shoujo is like girls romance right and it's very very much just like shounen-ai (literally identical) yet on that spectrum I guess there's echii/harams which can sometimes be wholesome and have a story but it guarantees implicit content such as yaoi 99% of the time

Now everything that contains BL scenes...
But the most correct definition would be like yaoi is the ones that have sexual issues more implicit... Then shounen ai would be non so implicit and more innocent without any sex stuff... But we (me too) make it be generalized.
Right?
I'm asking bc a girl was saying that yaoi is every type of(๑•ㅂ•)و✧ ... Bc I make a difference between shounen ai and yaoi to make it easy to understand.