Interesting point, but I'm pretty sure your first interpretation was what was intended, namely the 4th finger barre.
Mr. Delcamp sometimes proposes his own non-standard fingerings where he believes they serve a useful purpose. Here I would guess it is to ease a legato transition from the previous bar, by enabling the A to be held with the 2nd finger until the very last moment before playing the final chord (having already formed the chord shape), rather than having to lift that finger and move it two frets further up to play the chord in the more usual way. Mr. Delcamp's way is more difficult, admittedly, and that will be why he placed the rectangular outline around this chord, which is his method of indicating a particularly difficult passage that will need extra practice.
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