Try not to panic. Being handcuffed and removed from a cell happens for a wide range of reasons, most of which are not as serious as they look in the moment.
The most common explanations are a routine cell search or shakedown, a transfer to a different housing unit within the facility, a medical situation that requires attention, or a move to segregation pending an investigation into something that may or may not involve your husband directly. Facilities also pull inmates out for legal visits, court appearances, and administrative meetings. None of those require advance notice to family.
The fastest path to information is to call the facility and ask to speak with the captain on duty. The captain has oversight of what is happening on the floor and is the most direct source for a status update in a situation like this. Be calm and straightforward when you call. Explain who you are, who your husband is, and that you witnessed or were told he was removed from his cell and you are trying to understand what happened.
You may not get a detailed explanation, but you should be able to confirm that he is still at the facility, that he is safe, and in some cases what the general nature of the situation is.
If the captain is not available or will not give you anything useful, ask for the shift supervisor or the warden's office. Keep your tone cooperative throughout. Getting emotional or demanding on the phone tends to close doors rather than open them.