It'll be because it's CT linked. I did a double take at the Old Bailey as well, but they have the CT courts and CT judges I believe - I think I expected him to pop up at Exeter Crown but it makes sense.
Also the initial Mags hearing and Crown CAN be on the same day, I have definitely seen it myself, it's just that court time often doesn't allow for it. Especially if being produced from prison.
I'm willing to bet the CT aspect means the court not only made time, but the risk assessment for moving him between courts would have meant a request to minimise movements and making them less predictable in case of opportunity for a premeditated attack on the van / convoy.
ETA - for those unfamiliar, Crown Court has to order the remand in custody - it cannot be done by the Magistrates.
www.cps.gov.uk/prosecution-guidance/bail#c9