Does the term 'marginal' refer to the last consumer?
Yes marginal refers to the last or one more unit or person. I don’t see there any contradiction if you have 2 people in room and third person joins it’s both the last person and one more person.

If you are looking for a precise definition then in economics the concept of margin is connected to the first derivative (instantaneous rate of change) of function at some point. For example, with utility function $U=q^2$ marginal benefit of consuming 10 units of $q$ would be $U’(10)=2(10)=20$.

Also, demand curve is an aggregate of demands of individuals who all might derive different marginal benefit of consuming the good, the point of the answer is that the marginal customer, last customer to participate in the market, will have marginal benefit of consuming good exactly equal to price (since if $MB&lt;P$ the person would just not participate in market).