Kieran
Unfortunately you have confused the answer for one benefit with that for another, it's easily done
Rob's question was in regard to ESA which does not have special provisions for amputees whereas Mat's post was about PIP which does.
The rule for PIP is that a claimant must be able to put one biological foot on the ground in order to walk, if they cannot then they should automatically receive 12 points for this activity. So a double amputee will automatically qualify but a single amputee won't, the point of amputation is not relevant to the test.
Gordon