I have to agree that I wouldn't read much into a "yo" message, and saying "I'm sorry I was at work" isn't an "apology" per se, just more of a conversational statement, like "sorry I didn't get back to you", or "sorry I missed your call."
I wouldn't read too much into this.
Sounds like he was bored OR playing a joke on you OR accidentally texted you and meant to text someone else OR needed his ego boosted.
If he liked you in any real way you would have known it by now.
By the way, you have written about your boyfriend. Are you still dating him?
Because he knows you'd be thrilled to hear from him. Guys (and girls) like to feel like people have crushes on them. But since you've known him for a long time and this is out of the blue . .. I wouldn't think too much of it.
Anyway, he'd get the ego boost because you are flattered he wrote you and excited. That FEELS good but is different than his being excited to get in contact with you in the same way you are at hearing from him. Does that make sense to you?
How would that give him an ego boost?
If you've had a crush on him for ages and he knows it, and hasn't responded, my guess is he was looking for a little ego boost from you.