Yes it's pressed beef The old wrappers used to describe the process... something like this " Arby's invented the self basting roast beef. Selected chunks of beef are blended with chopped beef and food quality phosphate" YUUUUUMMMM sounds good doesn't it.... sorta like "Selected chunks of dog food are mixed with a specially selected Radioactive Isotope, and blended til you puke!"
A while back Arby's had an advertising campaign "America's Roast Beef, Yes Sir!" I used to sing along and sing "Artificial Roast Beef, Yes Sir" Occasionally I luck out and find a store which undercooks it's roast, which makes it tolerable.
Back in the early 70's the first time I went to an Arby's the hung an actual roast on a basket of Stainless steel chains it would spin in glass enclose, and it "roasted" on the counter using Infrared Lamps.
They would slice it as you watched, and put it on a bun and then use some steam table contraption to shoot steam into the bun. It tasted AMAZING! Why they would change this recipe, I'll never know ( yeah I know it was expensive ) Thing is, I'd pay twice as much to do it the old way. You can't tell me that this crap they serve now is that much cheaper than the old way.
When I moved to Las Vegas in the late 70's I was shocked to see no spinning roast beef and a very bland artificial roast beef in it's place.... I thought it was Just in Vegas, but going back home I found the same crap there.
Someone should find out the old recipe and open a "new Arbys"