Is sierpenski's triangle considered to be a computational model?
I would not call Sierpenski's triangle a computational model.  A computational model should be a system that has a way to compute something.  This means there needs to be a way to supply an input, and a way that the system does something with that input to compute something.  Sierpenski's triangle is a single thing (a single set), and it is fixed -- there is no way to supply different inputs and get a different output.

For similar reasons, I would not call Pascal's triangle a computational model.

However, I would call rule 90 a computational model.  There are standard ways of providing an input and computing stuff (e.g., the input bitstring is interpreted as a row, and then successive rows are derived using the cellular automaton rules, which is interpreted as a computation).  Similarly, I would call rule 110 a computational model.  Or, more generally, I might call cellular automata a computational model, and rule 90 and rule 110 as two instances of cellular automata.