Custom format/display of sums of vectors

According to Jason Harris's talk at Wolfram Technology Conference 2019, the way to do that is:

MakeBoxes[line[
    t_
    , p : _List /; VectorQ @ Unevaluated @ p
    , u :  _List /; VectorQ @ Unevaluated @ u
    ]
   , StandardForm] :=
  With[
   {argsp = Map[Function[{a}, MakeBoxes[a, StandardForm], HoldAll]
      , Unevaluated @ p, {1}]
    , argsu = Map[Function[{a}, MakeBoxes[a, StandardForm], HoldAll]
      , Unevaluated @ u, {1}]}
   , RowBox[{"(", "", GridBox[Transpose @ {argsp}], "", ")", "+", 
     MakeBoxes[t, StandardForm], "(", "", 
     GridBox[Transpose @ {argsu}], "", ")"}]
   ];

line[t, {1, 2, 3}, {-1, 0, 1}]

I'm a beginner on this subject, so there may be subtelties I'm not aware.