I do not understand quite what he means either. But everyone is assuming a three wheeler is a type of vehicle. It isn't, is what I am saying. So you need to know what you are comparing with what.
A loaded Reliant Ant, up to half a ton, depending on specs - probably including tyre recommendation, is not in the provisional driving category. So unless the 875 is overweight they are not the same. A comparison cannot be made. Without specs I do not know the weight of an unloaded Ant, so I do not know who can drive it, in that condition. From the off Reliant flirted with the weight limit, and if we get down to it, most are illegal in use, without a full licence. It has just been the case that the letter of the law has not been applied, as in the two other cases I mentioned previously. Indeed micronauts should be angry about that, as the opposition was able to gain unfair advantage, by not sticking to the rules. Its water under the bridge now, and Reliants themselves have become an endangered species.
A Scammel Scarab is a three wheeler. Most are not classed as such. They can be locomotives, thus allowing them to tow more than one trailer on the highways. I can drive one. I do not think most people under about 48 can. I am willing to bet a Scarab that is a locomotive, has a different spec to one that is not.
Might be fun to invite DVLA/VOSA inspectors to the National to see how many folk are illegal. We have not even touched trailers yet! Ignorance is bliss, to be honest. I am happy to leave cars standard unless I research a way to advance them that genuinely looks like an improvement worth the effort. That has become more sharply compared to other options outside microcars, as values have harmonised with other options for transportation.