'A tulwar is a tulwar, when it is a tulwar' - quite simple, dont you think?
The shown sword I will leave to Jim, and expect a lecture from him on the subject
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Tulwars are mostly described as having a relatively broad, slightly curved blade with a ricasso and a false edge. This is important, but what seems to be more important, is the tulwar hilt, as any sword with this kind of blade, but without the tulwar hilt is not a tulwar.
Some blades are slightly curved, while others are very curved - shamshir blades. Some have a ricasso while others dont - but they are still called tulwars. To this comes that there are other blade types used, but they are still called tulwars.
One type, where the hilt type does not make it a tulwar is, the belt sword. Here the blade is so flexible, that it can be used for a belt. This kind of sword is due to the flexibility very difficult to fight with, but the ones I have seen all have the tulwar hilt.