[
www.bartleby.com]
He is referring to "Homer sometimes nods", meaning that even the best folks sometimes make mistakes. The whole thing is,
Indignor quandoque bonus dormitat Homerus;
Verum opere in longo fas est obrepere somnum.
(It's a shame when even the worthy Homer nods, but one gets drowsy in so long a work.)
So Alex is saying with,
I know there are to whose presumptuous thoughts
Those freer beauties, ev'n in them, seem faults.
Some figures monstrous and misshaped appear,
Consider'd singly, or beheld too near,
Which, but proportion'd to their light or place,
Due distance reconciles to form and grace.
A prudent chief not always must display
His powers in equal ranks and fair array,
But with th'occasion and the place comply,
Conceal his force, nay, seem sometimes to fly.
Those oft are stratagems which errors seem,
Nor is it Homer nods, but we that dream.
It is not that a prudent chief's presumptuous thoughts are faults, but may also be dreams of what could/should be. Is that pure, unadulterated baloney? Yup.