It's not as simple as "Nothing happened"
They got naked and got into bed
Probably kissing and lots of touching all over
He gets erect - probably with help from her
Penny rolls the condom down his erection and he prejacs
So at this point the "encounter" stops, they do not have penetrative sex
But they were going to - they both full intended to
He got naked with Penny, got in bed with her, ran his hands all over he body, her breasts, probably her pussy, probably had his fingers inside her
Penny had her hands all over him, held his erection, masturbated him, maybe used her mouth on him - and used her hand to bring him to climax
So "nothing happened" ?
And yes, it all "happened" in Leonard's bed
No wonder Emily was so pissed when she found out as well .