Q: Is it normal for the manuscript status to become 'Under Review' on the submission day itself?

Both your assumptions could be true, or there could be some other possibility(ies).

So, it could well be a system error, and you’ll know whether this was the case if the status changes soon. It could be a reject too, due to the swift change, and you’ll know of this too soon. In case it’s a reject, based on how quickly the status changed, it’s probably due to a scope mismatch. As it’s a journal by T&F, which is a big publisher, the decision in case of a scope mismatch may be to ask you to submit to some other journal with them. On the positive side, it changed to ‘Under Review’ rather than directly to ‘Decision in Process.’ So, there may be some reason to hope. :-)

For now, it would not help to speculate on more possibilities and would be best to wait to hear from them next. In the worst case that it’s a desk reject though, as you may know, you may make changes to your manuscript based on any feedback you receive from here and submit elsewhere. Before submitting to the next journal though, it may help to first send them a presubmission inquiry in order to save your time and effort.

And to avoid/minimize desk rejection, you may find these resources useful:

• Does a direct 'Decision in Process' status indicate rejection?
• Most common reasons for journal rejection
• Tips to avoid journal rejection [Free ebook]

Hope that helps. All the best for whatever is next!