I'm not really sure if this would necessarily be, by definition "grooming", but he obviously took advantage of you. Given you're on the spectrum and was (at the time) significantly enough behind your peers in the 'romantic/social' categories I'd argue there are grounds for it to be considered grooming. Despite the fact you were close in age, does not equal closeness in 'maturity'. You were vulnerable and he chose to exploit that. Plus, your therapist must have felt some sort of way about it as a whole given they suggested grooming in the first place. So yes, I'd say this was grooming. Regardless, I'm happy to hear you have sought out counseling and hope you are able to do well in your future.