While I never would have responded the way he did, let me try to offer an alternative point of view as a seller. You said you asked questions and made an offer. He answered your questions and accepted the offer. While not legally binding, I consider this the internet equivalent of a handshake and would personally never back out after offering my hand. The time limit on the deal part isn't pushy in my opinion so much as prudent business practice. If sellers put an extended hold on animals every time an "offer" was made they'd miss out on a lot of sales due to animals being in limbo for folks who eventually ghost out.
It was nice of you to let him know you were backing out of the deal. I personally would have thanked you for informing me and moved on from there. I think it's a bit hypocritical to apologize several times to a person then write a bad review, especially as you are still apologizing to the subject of said review in your last correspondence. People generally don't apologize unless they feel they have wronged someone in some way. I think it's a good idea for you to avoid this seller as you obviously have different ideals when it comes to commerce. I personally would not avoid them based solely on the information given here. Then again, a lot of it has to do with wording, maybe I'd see your point of view better after reading the e-mails if you care to post them in their entirety.