Consult your advisor
Regardless of the specifics of your message - an offer to review a paper which you have not previously discussed and arranged with its originator is something to consider carefully. Perhaps the best person to give advice is not random academics on this site, but someone who knows your field, (likely) knows the person involved, knows the journal etc.
Of course - don't tell your advisor any details which should be kept confidential, like an author name, title of the paper etc.
In this specific case, consider rejecting.
he titled me "Dr. Monkia" although I am still being a graduate student.
Indeed, this is a warning light. It means the sender doesn't know who you are, but more significantly, did not bother to check whether your background is appropriate to write the review. If they had bother, they'd have figured out you're not a PhD yet.
He asked if I couldn't review, I can ask a qualified colleague to do so, or let him know immediately.
Did he now? That's cute. "Can you do my work for me? If you can't, won't you be so kind as to find some other sucker to do it and arrange for it to be done?"
This does not sound like something a serious editor would say. If I had no other information, I would probably reject merely because of this sentence.
Of course, I am interested in the paper's topic, but I don't consider myself an expert.
So, this is not a good enough reason to reject review requests. On every specific subjects of a paper, only a handful of people in the world are experts (well, depending on the discipline I guess; it's like that a lot in Computer Science); and often none of them is available to review the paper. So people with related expertise have to do it. This also has some positive aspects, such as assessing applicability and relevance beyond the clique of those few people.
Bottom line: Unless your advisor, or people very familiar with that Professor or journal say otherwise, I'd be hesitant to accept.