I am not familiar with the semi dwarf bougainvilleas, but I have a "Dwarf variety", not sure if this is what they are calling semi dwarf? The leaves and flowers are smaller than the regular ones. That's the easiest way for me to tell the difference. Mine does grow a little slower than the regular one...

Here is a link that might be useful: {{gwi:1315358}}

Hi
Bougainvillea can be grown at almost any size using standard "Bonsai "techniques as well as standards and topiary. Right pot and clipping at the right time will produce almost any size and shape you desire. Except for extreme cold they are the worlds most tolerant plants lol.
There are hundreds of hybrids ,grafted,double flowering as well as color changing types.
They make wonderful oversize pot plants . Terrible garden plants due to the thorns lol. gary