He is in much more trouble of filing a false police report which is a felony. His mailing of a threat letter which contained white powder is a serious federal felony, and his other activities to purchase materials, pay people, etc to orchestrate the entire "attack" are several steps beyond filing a false police report.
Smollett threat letter called "enormous mistake"; Purported attack location identified; Federal charges "certain"
http://www.cwbchicago.com/2019/02/smollett-threat-letter-called-enormous.html
FBI Investigating if Jussie Smollett Sent Hate Mail to Himself
https://www.advocate.com/news/2019/2/19/fbi-investigating-if-jussie-smollett-sent-hate-mail-himself
Feds investigating whether Jussie Smollett played a role in sending threatening letter sent to 'Empire' studios addressed to him
https://abcnews.go.com/culture/stor...lett-played-role-sending-threatening-61161589
As of now he is not facing charges for that.The grand jury hearing is for filing a false police report.