There are two main reasons why it's not an issue that (D) references moving animal populations from one area to another:
1. (D) specifies this is something hunter-gatherer
societies do, which aligns with the stimulus' conclusion that the society in question was a hunter-gatherer society. Strengthen questions fall into the "Help" family of questions, so we accept the information in the answer choice to be true. If the answer choice says hunter-gatherer societies practice some activities we might commonly associate with agriculture, it's not our job to pick that apart! We accept that this is something hunter-gatherer
societies do and focus on the task at hand: asking ourselves if this answer choice strengthens the argument by at least 1%.
2. Even if moving animal populations from one area to another were to constitute 'agriculture' in some regard, the author disagrees with those who suggest the burned areas of land indicates "large-scale
agriculture" in the society, not 'agriculture' as a whole. Where is the line between some sort of loosely agricultural activity and large-scale agriculture? Do hunter-gatherer societies unequivocally engage in no activity reminiscent of agriculture whatsoever? We don't know!
Long story short, the phrasing of the answer choice and the stimulus make it so that (D) does not weaken the conclusion. Instead, (D) strengthens the conclusion by offering a reason why hunter-gatherer societies might burn a large area of land.
I hope this helps