Yeah, the size of the plume (and blackness of the smoke) does indeed have something of a space-rocket.
But I dont know whether an ABM needs such a big rocket booster. That is, if the HQ-26 really is the ABM missile...
From the comments in the weibo, most seem to say that it might be a Chinese SM-6 equivalent. Maybe with secondary ABM capability.
The black smoke I think is simply from the cold launch system ejecting the missile out of the tube... trying to gauge its role simply based on appearance of the smoke plume or even simply based on the missile's appearance with or without booster is not really useful either, because both naval SAM and ABM weapons can look identical (re: SM-3 variants and SM-1/SM-2/SM-6).
In this case I think we should be deferring to credible rumours if there are any, and if there are not then we should consider what the consensus on the BBS may be while also using common sense on our own.