SPOILERS

This one ended up being a bit trickier than I anticipated in part 2, but eventually I got it:

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Linq;
namespace advent_of_code_2020
{
    class Day2
    {
        protected List<String> PuzzleInput = new List<String>() { ... };

        public void solve()
        {
            part1();
            part2();
        }

        public void part1()
        {
            var correctPasswords = new List<Password>();
            foreach (string password in PuzzleInput)
            {
                var testPass = new Password(password);
                if (testPass.IsValid())
                {
                    correctPasswords.Add(testPass);
                }
            }
            Console.WriteLine("The answer to part 1 is {0}", correctPasswords.Count);
        }

        public void part2()
        {
            var correctPasswords = new List<Password>();
            foreach (string password in PuzzleInput)
            {
                var testPass = new Password(password);
                if(testPass.IsValid2())
                {
                    correctPasswords.Add(testPass);
                }
            }
           Console.WriteLine("The answer to part 2 is {0}", correctPasswords.Count);
        }

    }

    class Password
    {
        public int PasswordMin;
        public int PasswordMax;
        public string Letter;
        public string PasswordString;
        public string InputString;
        public char Position1Char;
        public char Position2Char;

        public int CharacterFrequency;
        public Password(string inputString)
        {
            InputString = inputString;
            SetProperties();
            SetPositionChars();
        }

        protected void SetProperties()
        {
            var matches = Regex.Matches(InputString, @"(\d*)[^-](\d*)[^ ](\w*)");
            PasswordMin = Int32.Parse(matches[0].Value.Split('-')[0]);
            PasswordMax = Int32.Parse(matches[0].Value.Split('-')[1]);
            Letter = matches[1].Value.Replace(" ", "");
            PasswordString = matches[2].Value.Replace(" ", "");
            CharacterFrequency = PasswordString.Split(Letter).Count() - 1;
        }

        public bool IsValid()
        {
            return CharacterFrequency >= PasswordMin && CharacterFrequency <= PasswordMax;
        }

        public bool IsValid2()
        {
            var letter = Convert.ToChar(Letter);
            if( letter == Position1Char && letter != Position2Char)
            {
                return true;
            }

            if( letter == Position2Char && letter != Position1Char)
            {
                return true;
            }
            return false;
        }

        protected void SetPositionChars()
        {
            var letter = Convert.ToChar(Letter);
            if( (PasswordMin - 1) <= PasswordString.Length )
            {
                Position1Char = PasswordString[PasswordMin - 1];
            }
            if( (PasswordMax - 1) <= PasswordString.Length )
            {
                Position2Char = PasswordString[PasswordMax - 1];
            }
        }
    }

}