one post only !
The straight answer to your question is "No", there was no such indication in that article..
However, I infer from a BA statement of two weeks ago that they are likely to be the longhaul aircraft that landed at LHR/LGW on the evening of April 20 when UK airspace was first reopened, i.e.B747/767/777. Can anyone else confirm this ?
It might be of interest to recall that on that day the UKMO chart forecast of possible ash in the height band SFC-FL200 showed it covering not only the UK but most of western and some of central Europe. At the same time Eurocontrol had published a chart showing areas of forecast high ash concentration that could have presented a safety issue. This chart looked totally different. The areas affected were confined to the Atlantic, i.e not over UK or Western Europe at all.
And this helps explain BA's rationale in dispatching those flights. They were planned to land if necessary at other European airports, and some did just that, in Ireland, France, Belgium, Netherlands Germany and Spain because all that airspace was already open based presumably on the Eurocontrol forecast, not the UKMO version on which the British authorities were relying. And then UK airspace opened....