My son was exactly the same at two, he had no idea what a birthday was but he absolutely loved anything with wheels! We ended up just doing a simple outing to a place he genuinely enjoyed, which made it feel really special even without the big party fuss.
Since your boy is into cars, maybe look into places like KidZania or even a simple trip to watch the cars at a carpark rooftop or near the expressway, toddlers that age honestly get so excited just seeing real vehicles up close. You could round the day off with a small cake at home with just the immediate family, keep it cosy and low-key, and he will still feel the love without being overwhelmed. Hope you both have a really lovely day celebrating him!