It’s certainly possible, but the lock grease we use is kind of a yellowish color like that so it could just be excess grease working its way out over time, and the marks might have always been there – once someone becomes suspicious of a piece of hardware they tend to see all sorts of little scratches and dings and such that they never noticed before.
Still, even if it was tampered with, that’s a fairly decent padlock and Yale keyways are reasonably difficult to lockpick compared to Kwikset and Master’s garbage or even the average Schlage lock, so if nothing was stolen and the key still works without any weird catch or roughness, I wouldn’t worry about it. If the key doesn’t work (or if you’re still worried), you can bring it to a locksmith’s shop and they can at the very least look down inside the keyway to see if the pins are all moving properly and there’s no debris or anything broken off inside there.
You could simply replace it with an even tougher padlock of course, but if the would-be thief returns, they might see that better padlock and think “Oh ho! So they’ve got something in there that they really don’t want stolen, huh?” and decide it’s worth the time to search for another way in.
If you’re genuinely trying to secure something, I’d recommend calling a knowledgeable locksmith out and take a look at the area as a whole (rather than just the lock by itself) so they can point out any other potential ways a thief might enter that you don’t know about. Nothing can be 100% safe from forced entry, but you can fix easy exploits and make it difficult enough not to be worth the risk.