Can pulling samples cause oxidization?

Just wondering because I've pulled 2 samples at 1 week and 2 1/2 weeks and hit my gravity but when I bottled, it had strange, lingering, i-guees-cardboard-taste, almost like plastic, when I took a nip of the wort from the bottling bucket. It wasn't there before with my two sample pulls. I used DME, boiled for 5 min to bottle.

Even if pulling samples doesn't cause O2 to get into the carboy, can you still take precautions and purge the carboy with CO2 after you take a sample? What else can you do to prevent oxidation after fermentation is complete? if anything at all.

If you took your "nip" from the bottom of the bucket it might have been yeast bite?

I only re-blanket with co2 if I've pulled a large sample (12oz or more).

I wouldn't worry about it, there's very little chance sneaking a sample caused enough oxidation to detect. Young beer can just taste funny, I'd bet money it will get better with age not worse. Carbonation will also change the flavor quite a bit in a few weeks.