Yes.
I talked about it in that post. I even MENTIONED it in that post.
Slidecasting is when the cast time of an action is less than the GCD, allowing you free movement from (actually just before, but this is latency dependent) the cast ends until the GCD has completed and you can begin casting your following spell. All spells with cast times tend to have around a 0.5 sec window (again, depending on latency) to do this in. Spells with a cast time longer than the GCD don't typically allow much room for movement before the GCD can be activated for the next spell (High Fire/Blizzard have 3 sec cast times, for example, Fire 4 has a 2.8 sec cast time, and SMN's Slipstream has a 3.0; also RDM's Thunder/Aero if you're playing extremely poorly or your latency keeps failing to register your Dualcast buff), resulting in clipping. BLM main spells take up the entire GCD, leading to them having a very narrow slidecast window vs WHM's 1.5s casts, which allow for move movement. Even if we're talking Cure 2 and Medica, WHM still has a bigger slidecasting window than BLM's very much smaller one.
Both Jobs don't handle long movements with slidecasts, though, they handle them with instant casts or a lot of stutter-stepping prepositioning, and in BLM's case, its various instant cast tools and Aetherial Manipulation.
.
Maybe don't call people out on things they can school you on.
EDIT:
Bonus knowledge, since you are ill informed and probably could use a little education on the topic:
oGCDs have an approximately 0.7 sec animation lock (again, latency comes into play), as do normal abilities, meaning between the normal ability (0.7), first weave (1.4) and second weave (2.1), you can't weave a third oGCD without clipping into the next GCD. While there are occasions to do this, it's a DPS loss when avoidable. Spells with a 1.5 sec cast time can only have a single weave (2.2 sec total), and this is also true of RDM's 1-2 of their melee combo, which have a shortened 1.5 sec GCD allowing only single weave (0.7 for the melee animation, 1.4 by the end of the weave), which isn't true of the third strike (2.2 sec, which allows two weaves leading to 2.1 if you have low latency of less than 0.1 sec); SMN also has this during Garuda (Emerald Ruin/Rite/Catastrophe also only have 1.5 sec CDs, not that you have a lot you'd be weaving there anyway).
Also note that GAP CLOSERS have slightly longer animation lock as well, briefly preventing movement in addition to the effects.
Consider yourself informed, now.
(Seriously, people need to stop rushing for a "gotcha" so hard they step into being extremely easily schooled.)
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EDIT2:
(Change: Slipstream's cast is 3.0, not 3.5)
Seriously, people need to stop rushing for a "gotcha" so hard IN GENERAL.