Lincoln had extended his blockade to Virginia over a month earlier and well before Virginia had voted to secede. Virtually every precedent in the history of warfare considers a blockade to be an overtly hostile act of war. You are also incorrect about the date of the army's arrival in Virginia. The yankee army of 10,000 men marched into Alexandria on May 24th.
What about armed invasion and takeover of miltary posts and other government installations? Which started clear back in 1860, all over the South. Were those also acts of war? The Union chose not to consider them such, but maybe they just weren't as "sensitive" as southerners.
I'd like a reference on the Union blockade of VA before secession. It's contrary to some things I've read elsewhere.
Thanks for your correction of the date on "invasion" of VA.