Is it possible to make a decision upon a manuscript just within a month?

I cannot make any statement about this journal and this may depend somewhat on the field, but so far I never spent more than a day’s work on any review. The main problem why reviews take so long is not that the review itself actually takes that long, but that reviewers need to find time for the review given their numerous other duties.

Therefore it’s entirely possible that a referee reviews a paper within a day – maybe somewhat more, depending on the field – if they have time at hand. This needs not have to do anything with the review being sloppy or the paper being bad; it’s just a question of luck. I know of one example where a paper for Physical Review Letters (a high-level physics journal) went from submission to publication in something around ten days. Also, one of my papers once received a positive review within four days.

If the journal expects the review process to take eight to ten weeks, then a month sounds entirely plausible. It’s not even outstandingly short.

I don't know that specific journal but, for instance, the IEEE Transaction on Instrumentation and Measurements ask the reviewers to complete their reviews in one month (reviewers can ask for a few weeks' extension). So, typically, you can expect the reviews to arrive within 4-6 weeks, even in case of long papers.

You'd have to ask the journal how they do it.

Think how long you'd take to review such a paper on a subject you know intimately. Note that "review" doesn't necessarily mean "read with utmost care, check each statement/proof/program carefully", it will lean more to "check if this seems to make overall sense, has the author shown knowledge of the techniques in use, does this look too simple or is it perhaps something well-known", i.e., is it a worthwhile step forward, plain nonsense, or just a rehash.