Nurble PHP vs C#

nurble.cs

using System;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

class Nurblizador
{
    private static string[] _nouns = File.ReadAllText("nouns.txt").Split("\n");

    static string Nurble(string text)
    {
        var pattern =  Regex.Split(text.ToLower(), "[^a-z]")
            .Where(w => !string.IsNullOrWhiteSpace(w))
            .Distinct()
            .Join(_nouns, n => n, n => n, (w, n) => $@"\b{n}\b")
            .Aggregate((a,b) => $"{a}|{b}");
        var replacement = @"<span class=""nurble"">nurble</span>";
        return Regex.Replace(text.ToUpper(), pattern, replacement, RegexOptions.IgnoreCase).Replace("\n", "<br>");
    }
}

nurble.php

<?php
function nurble($text)
{
    $nouns = file('nouns.txt', FILE_IGNORE_NEW_LINES);
    $isMatch = (bool) preg_match_all('/\b[a-zA-Z]+\b/', $text, $matches);
    if ($isMatch === true) {
        $words = array_unique(
            array_filter($matches[0], function ($word) use ($nouns) {
                return  in_array($word, $nouns) === false;
            })
        );
        $pattern = sprintf('/(\b)%s(\b)/', implode('(\b)|(\b)', $words));
        $replacement = '\1<span class="nurble">nurble</span>\2';
        $text = preg_replace($pattern, $replacement, $text);
    }
    return str_replace("\n", '<br>', $text);
}
?>