Number changing to a table when passed into a function?

So I currently have this code here:

if bestMatchId == nil then
            local NewMatch = { Players = {}, MapId = map, updateFunc = function(match, matchPos)
                print("Firing update func with id", matchPos)
                MatchmakingService:FireAllClientsEvent(UPDATE_MATCH_DETAILS_EVENT, matchPos, match.MapId)
                if #match.Players >= 1 then
                    wait(5)
                    local TS = game:GetService("TeleportService")
                    local CodeSuccess
                    local TSCode
                    local Attempt = 0
                    repeat Attempt = Attempt + 1 CodeSuccess, TSCode = pcall(function() TS:ReserveServer(PlaceIds[map]) end) until CodeSuccess == true or Attempt > 5
                    -- Teleport players
                    local TPSuccess, TpMessage
                    local TpAttempt = 0
                    repeat TpAttempt = TpAttempt + 1 TPSuccess, TpMessage = pcall(function() TS:TeleportToPrivateServer(PlaceIds[map], TSCode, match.Players, "Start", {}) end) if TPSuccess == false then warn("TP ERROR:", TpMessage) end until TPSuccess == true or TpAttempt > 5
                    Matches[matchPos] = nil
                end
            end }
            table.insert(NewMatch.Players, player)
            local pos = table.getn(Matches[map]) + 1
            table.insert(Matches[map], pos, NewMatch)
            bestMatchId = pos
            print("Firing update func with pos", pos)
            NewMatch:updateFunc(NewMatch, pos)
        end

It pretty much makes a new dictionary that represents a match, and it has a update function that is called each time the match is updated. When the match is initially created, it's inserted into the main table with all matches, and then prints "firing update func with pos insert pos in main table here", but in the update function itself when I run print("Firing update func with id", matchPos) it prints out that the matchPos part is a table, leading me to believe at some point Roblox is converting my number to a table somehow.