Unusual notation in Moyreau Pièces de Clavecin

What do you all make of the last few measures in the right hand, shown in the attached file? This is from the Concerto that concludes Moyreau’s third book. My best guess is that these are meant as arpeggiated chords (I don’t know why Moyreau didn’t use one of the signs that other composers employed for arpeggiation). I toyed with the idea that they represent triplets; however, elsewhere Moyreau does notate triplets in the usual way, albeit without the numeral ‘3’. Moyreau concerto 1st mvt|690x255

What would be the difference between the then-fashionable Italian-style hurried triplets and arpeggios anyway?

Not much, particularly at a very fast tempo.

If they do represent triplets (“hurried” or not), why not notate them in the usual way? Do the beams and slurs mean that he wanted them played very legato, maybe even held down? I’m really guessing here, since I’ve never seen this before. I hope someone has and can explain it.

He did not notate them in the usual way because the meaning is different. Rameau clearly explained (and to an extent this applies generally to late French Baroque music) that the slur, when applied over a broken chord, means not just overlegato but to keep all the notes down: a slow arpeggio.