As to whether this was perhaps a deposition related to the family's civil wrongful death suit against CW, I don't think so.
It was reported that around 2/13/19, family Attorney Lambert was in contact with CW, and confirmed that CW was not fighting/contesting their civil wrongful death action. In fact, CW never hired an attorney, did not respond to the legal complaint timely, and essentially allowed for a default judgement. Based on this information alone, it's doubtful that there was ever a "deposition."
However, in announcing CW was not fighting the wrongful death action, Attorney Lambert also reported that he was most surprised by CW's cooperation, and his openly answering his questions. He stated he believed that CW had come to accept liability for his criminal actions.
CW relationship with the FBI/CBI/and Frederick PD (the reported interviewers) was tied only to CW's criminal matter (his murder charge and conviction).
Perhaps it was mere coincidence that the multi-agency interview with CW reportedly happened only days later around 2/18/19.
I am curious whether or not SW's family contacted the criminal investigators to request they interview CW given that he was extremely forthcoming with their civil suit attorney. (Or maybe Lambert suggested CW contact investigators).
It's probably irrelevant how it went down, but I believe more than anything, SW's family wanted only one thing from CW and that was for CW to put an end to the ugly, hurtful, speculation that SW killed her children.
MOO
ETA:
Lambert expected a conversation with Watts to be awkward, and possibly even “eerie.” However, when on the phone, Lambert suggested Watts may have come to terms with his new reality, as he answered every question they had openly.
“It wasn’t weird, or anything… He doesn’t seem to be fighting this,” Lambert said. “(Watts is) admitting liability, or giving up things that he might’ve had claim to.”
Lawyers: Shanann Watts’ Parents Lawsuit To Go Uncontested By Chris Watts
Chris Watts not fighting wrongful death lawsuit filed by Shanann Watts’ family