The Septuagint is different from the Hebrew and draws from a different Hebrew manuscript tradition than the Masoretic Hebrew of today, but the Vulgate draws from both (particularly in the Psalms). This has an effect both on Hebrew wording and on the reading of Hebrew words. This has not traditionally been seen as a drawback; the Septuagint has been regarded as a particularly holy and useful translation by Christians, and was of course the Bible version most familiar to Greek-speaking Jews and Early Christians. (Which was pretty much everybody.) It tells us how the pre-Christian Jews translating the Septuagint thought the Hebrew Bible should be interpreted. That’s why it’s traditional to read Greek, Latin, and English versions of the Bible side by side, when studying a passage.
Here’s what the NETS translator of the Septuagint has to say about verb translation from Hebrew to Septuagint Greek:
In the Septuagint, “the Hebrew verbal categories of tense-aspect presented something of a problem to the Greek translator…” So the translator chose default equivalents and stuck with them. “Thus Hebrew yiqtol forms are usually translated by the Greek future indicative, the qatal by the aorist indicative, and the participle often by the present indicative. It should be noted, however, that participles are also often translated by participles, even though that may produce either strained syntax in the Greek or an obvious change of syntax… the defaults produced a certain stiltedness and abruptness in the use and sequence of Greek tenses.”
He also says that tons of different Hebrew words get translated into Greek as being about “help” or “support” or “shelter”.
So the excruciatingly literal NETS translation of your line in Septuagint Greek is:
“He who lives by the help of the Most High,
in a shelter of the God of the sky he will lodge.”
Welcome to the wonderful world of Bible translation!