Reading the article, I don't see Walker complaining, to be honest. Here's a quote from the O-line coach:
He mentioned being challenged, being the best man on the roster for the job, and that there was nothing he could do about the situation.
If I was to paraphrase Walker, it'd be "I'm not promising I'll be an all-pro, but I'll take on the job and do my best because the team asked me to make the switch from my normal position."